1. Field of the Invention
The present invention relates to an iamge processing method for electrically processing image information and an apparatus therefor.
2. Description of the Prior Art
There are already known various apparatus for storing digital image data, obtained from a solid-state imaging device such as a charge-coupled device, a television camera or a scanner in a semiconductor memory, a magnetic disk or a magnetic tape, and reproducing the thus stored data in the form of dots or small picture elements by means of a laser beam printer, an ink jet printer, a thermal printer or the like.
Such conventional apparatus requires a memory of a very large capaciry for storing the image data, for example a capacity of 4072 kilobits for storing the data of an original image of A4 size (215.times.296 mm) with a resolving power of 8 lines/mm, or a capacity of 1.6 megabits for the same purpose with a resolving power of 16 lines/mm. Also for achieving high-speed data reading and printing, the memory has to be of a high-speed capability and has therefore to be made of a semiconductor memory. However the semiconductor memory, if used in such very high capacity, is inevitably expensive and becomes bulky in circuitry.
The reproduction of an intermediate tone from digital image data in such apparatus generally relies on a so-called dither method in which the image density is controlled by the change in the number of dots to be recorded in a unit area. However, such intermediate tone reproduction by the dither method inevitably involves distortion in the image edges or formation of moire patterns, and requires a complicated circuit involving a comparator and a memory for storing dither patterns.